The Formation and Cleavage of Lysinoalanine Crosslinks

Abstract

Treatment of lysinoalanine (LAL) with methyl iodide at pH-values above 8 leads to cleavage to dehydroalanine (DHA) and Nε-di- or/and trimethyllysine, as was shown by ultraviolet spectra and amino acid analysis. This reaction is due to methylation of the crosslinking NH group of LAL to the quaternary ammonium compound; nucleophilic β-elimination follows. By this reaction, the ε-amino groups of polylysine and its copolymers can be methylated to form di- and/or trimethyl-lysine residues. Chemically modified polypeptides containing Nε-dimethyllysine can be made in this way.